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            <h1 style="display: none">流程控制</h1>
            
              <p class="note note-info">
                
                  
                    本文最后更新于：2023年5月23日 晚上
                  
                
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                <h1 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h1><p>必会内容</p>
<p>流程控制，包含：</p>
<ul>
<li>条件控制</li>
<li>循环控制</li>
<li>异常管理</li>
</ul>
<h1 id="条件控制"><a href="#条件控制" class="headerlink" title="条件控制"></a>条件控制</h1><h2 id="if"><a href="#if" class="headerlink" title="if"></a>if</h2><p>拥有以下关键字：</p>
<ul>
<li>if，条件起始，必写</li>
<li>else if，又或者，多个else if 由上至下判断，只能有一个if或else if生效。非必写</li>
<li>else，否则。if和else if都不成立时运行，非必写</li>
</ul>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">const</span> a = <span class="hljs-number">1</span><br><br><span class="hljs-keyword">if</span> (a == <span class="hljs-number">1</span>)&#123;<br>  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;a为1&quot;</span>);<br>&#125;<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span>(a == <span class="hljs-number">2</span>)&#123;<br>  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;a为2&quot;</span>);<br>&#125;<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span>(a == <span class="hljs-number">3</span>)&#123;<br>  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;a为3&quot;</span>);<br>&#125;<span class="hljs-keyword">else</span>&#123;<br>  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;a不为123&quot;</span>);<br>&#125;<br></code></pre></td></tr></table></figure>

<h2 id="三元运算符"><a href="#三元运算符" class="headerlink" title="三元运算符"></a>三元运算符</h2><table>
<thead>
<tr>
<th>运算符</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td>条件?true:false</td>
<td>根据条件的结果判断，条件结果为true，则返回冒号左边的结果，否则返回冒号右边的结果</td>
</tr>
</tbody></table>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">const</span> a = <span class="hljs-number">1</span><br><br><span class="hljs-keyword">const</span> b = a == <span class="hljs-number">1</span> ? <span class="hljs-string">&quot;a为1&quot;</span> : <span class="hljs-string">&quot;a不为1&quot;</span><br></code></pre></td></tr></table></figure>

<h2 id="switch"><a href="#switch" class="headerlink" title="switch"></a>switch</h2><p>一般用来判断同类型的不同值，比如周几</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">const</span> weekDay = <span class="hljs-number">1</span><br><br><span class="hljs-keyword">switch</span>(weekDay)&#123;<br>  <span class="hljs-keyword">case</span> <span class="hljs-number">1</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周一&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-keyword">case</span> <span class="hljs-number">2</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周二&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-keyword">case</span> <span class="hljs-number">3</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周三&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-keyword">case</span> <span class="hljs-number">4</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周四&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-keyword">case</span> <span class="hljs-number">5</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周五&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-keyword">case</span> <span class="hljs-number">6</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周六&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-keyword">case</span> <span class="hljs-number">7</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周日&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>  <span class="hljs-attr">default</span>: <br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天不正常&quot;</span>);<br>    <span class="hljs-keyword">break</span><br>&#125;<br></code></pre></td></tr></table></figure>

<p>注意！！break关键字必须要加<br>如果没有break，会从条件的case开始，每个case都会执行</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">const</span> weekDay = <span class="hljs-number">2</span><br><span class="hljs-keyword">switch</span>(weekDay)&#123;<br>  <span class="hljs-keyword">case</span> <span class="hljs-number">1</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周一&quot;</span>);<br>    <br>  <span class="hljs-keyword">case</span> <span class="hljs-number">2</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周二&quot;</span>);<br>    <br>  <span class="hljs-keyword">case</span> <span class="hljs-number">3</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周三&quot;</span>);<br>    <br>  <span class="hljs-keyword">case</span> <span class="hljs-number">4</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周四&quot;</span>);<br>    <br>  <span class="hljs-keyword">case</span> <span class="hljs-number">5</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周五&quot;</span>);<br>    <br>  <span class="hljs-keyword">case</span> <span class="hljs-number">6</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周六&quot;</span>);<br>    <br>  <span class="hljs-keyword">case</span> <span class="hljs-number">7</span>:<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天周日&quot;</span>);<br>    <br>  <span class="hljs-attr">default</span>: <br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">&quot;今天不正常&quot;</span>);<br>&#125;<br><br><span class="hljs-comment">// 输入结果</span><br><span class="hljs-comment">/*</span><br><span class="hljs-comment">今天周二</span><br><span class="hljs-comment">今天周三</span><br><span class="hljs-comment">今天周四</span><br><span class="hljs-comment">今天周五</span><br><span class="hljs-comment">今天周六</span><br><span class="hljs-comment">今天周日</span><br><span class="hljs-comment">今天不正常</span><br><span class="hljs-comment">*/</span><br></code></pre></td></tr></table></figure>

<h1 id="循环控制"><a href="#循环控制" class="headerlink" title="循环控制"></a>循环控制</h1><h2 id="for"><a href="#for" class="headerlink" title="for"></a>for</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">const</span> lst = [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>]<br><br><span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> i = <span class="hljs-number">0</span>; i &lt; lst.<span class="hljs-property">length</span>; i ++)&#123;<br><br>&#125;<br><br><span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> idx <span class="hljs-keyword">in</span> lst)&#123;<br><br>&#125;<br><br><span class="hljs-keyword">const</span> dic = &#123;<br>  <span class="hljs-attr">name</span>: <span class="hljs-string">&#x27;muzhou&#x27;</span><br>&#125;<br><br><span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> key <span class="hljs-keyword">in</span> dic)&#123;<br><br>&#125;<br><br></code></pre></td></tr></table></figure>

<h2 id="while"><a href="#while" class="headerlink" title="while"></a>while</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">const</span> a = <span class="hljs-number">1</span><br><span class="hljs-keyword">while</span>(a == <span class="hljs-number">1</span>)&#123;<br>    <span class="hljs-comment">// 条件每次为true，则执行花括号代码.</span><br>&#125;<br></code></pre></td></tr></table></figure>

<h2 id="do…while"><a href="#do…while" class="headerlink" title="do…while"></a>do…while</h2><p>比较少用的循环</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">do</span>&#123;<br>    <span class="hljs-comment">// 不管任何情况先执行一遍花括号代码，</span><br>    <span class="hljs-comment">// 当条件为true，则再次执行花括号代码，直到条件为false</span><br>&#125;<span class="hljs-keyword">while</span>(条件);<br></code></pre></td></tr></table></figure>

<h2 id="循环中断"><a href="#循环中断" class="headerlink" title="循环中断"></a>循环中断</h2><ul>
<li>continue，在循环中停止继续执行本轮代码，跳到下一轮循环中。触发时，位于continue下的代码不执行</li>
<li>break，在循环中停止当前循环的代码，跳出循环。触发时，位于break下的代码不执行</li>
</ul>
<h1 id="异常捕获"><a href="#异常捕获" class="headerlink" title="异常捕获"></a>异常捕获</h1><h2 id="异常捕获处理"><a href="#异常捕获处理" class="headerlink" title="异常捕获处理"></a>异常捕获处理</h2><p>js中提供了三种异常处理的写法：</p>
<ol>
<li><code>try...catch</code></li>
<li><code>try...finally</code></li>
<li><code>try...catch...finally</code></li>
</ol>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">try</span>&#123;<br>   <span class="hljs-comment">// 尝试执行的代码</span><br>&#125;<span class="hljs-keyword">catch</span>(e)&#123;<br>   <span class="hljs-comment">// 异常处理,e 表示异常对象，或者异常结果</span><br>&#125;<br><span class="hljs-keyword">finally</span>&#123;<br>   <span class="hljs-comment">// 不管try语句块代码是否执行成功，都会执行finally中的代码</span><br>&#125;<br></code></pre></td></tr></table></figure>

<h2 id="手动抛出异常"><a href="#手动抛出异常" class="headerlink" title="手动抛出异常"></a>手动抛出异常</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">throw</span> 异常表达式;<br><span class="hljs-keyword">throw</span> <span class="hljs-string">&quot;Error2&quot;</span>; <span class="hljs-comment">// 抛出了一个值为字符串的异常</span><br><span class="hljs-keyword">throw</span> <span class="hljs-number">42</span>;       <span class="hljs-comment">// 抛出了一个值为整数 42 的异常</span><br><span class="hljs-keyword">throw</span> <span class="hljs-literal">true</span>;     <span class="hljs-comment">// 抛出了一个值为 true 的异常</span><br></code></pre></td></tr></table></figure>

<h2 id="自定义异常对象"><a href="#自定义异常对象" class="headerlink" title="自定义异常对象"></a>自定义异常对象</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><code class="hljs javascript"><span class="hljs-keyword">function</span> <span class="hljs-title function_">TestException</span>(<span class="hljs-params">msg</span>)&#123;<br>  <span class="hljs-variable language_">this</span>.<span class="hljs-property">msg</span> = msg<br>&#125;<br><br><span class="hljs-keyword">try</span>&#123;<br>    <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TestException</span>(<span class="hljs-string">&quot;报错啦&quot;</span>)<br>&#125;<br><span class="hljs-keyword">catch</span>(e)&#123;<br>    <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(e.<span class="hljs-property">msg</span>);<br>&#125;<br></code></pre></td></tr></table></figure>
                
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